From nobody Thu Apr 9 12:08:21 2026 Received: from ewsoutbound.kpnmail.nl (ewsoutbound.kpnmail.nl [195.121.94.186]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 061B520D4FF for ; Mon, 2 Mar 2026 13:17:54 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=195.121.94.186 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1772457477; cv=none; b=Xj314YVbEl423LE316pLZGLOYUfsl99j9ntFTPbuAaH2NkQ3CwhOcWqzuJQJE8NMMe5aoDJRSw9Zne4qwuhg7AZCFRuyATkjFOn9HbyectzKC6oHv+bJWqH/uTLVoeiaSUJDUsuzmyOb+NJczLW2uCjkX+LodD1UFQVUSGyWgD0= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1772457477; c=relaxed/simple; bh=HvN+5WSDnnaMmBob8vPdPAy1L1OeRTuABSQ4GCZi6gw=; h=From:To:Cc:Subject:Date:Message-ID:MIME-Version; b=jIKBYUk+Fw2LgNh34QoGR/J63Hfe7L6BjNZp8C9nd+QzzgFk4+QxNOUtN7rxFtwoq6fKxjOvObV8EUnDGWZjhOJ6MiydYCJksitgK1SFK4hX7tHFuQp4JVu+l/bt/RQ1t060LPftMLqx6aoEYZKfXmCP3mTWzbOHDqCqyfD4WVw= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=xs4all.nl; spf=pass smtp.mailfrom=xs4all.nl; dkim=pass (2048-bit key) header.d=xs4all.nl header.i=@xs4all.nl header.b=nKDgCSEM; arc=none smtp.client-ip=195.121.94.186 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=xs4all.nl Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=xs4all.nl Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=xs4all.nl header.i=@xs4all.nl header.b="nKDgCSEM" X-KPN-MessageId: 0fe854ce-163a-11f1-89dd-00505699b430 Received: from smtp.kpnmail.nl (unknown [10.31.155.8]) by ewsoutbound.so.kpn.org (Halon) with ESMTPS id 0fe854ce-163a-11f1-89dd-00505699b430; Mon, 02 Mar 2026 14:16:45 +0100 (CET) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=xs4all.nl; s=xs4all01; h=mime-version:message-id:date:subject:to:from; bh=UXOUq0SPuTwj8yiZauBk+IGzhYE4jhkwANNAtQNGrwo=; b=nKDgCSEMFuPHLhkvzBBa7QoiJn/nK64ml2iiskFgSL5fh+wFZ1trcdNR/IBkZuxJIAVl6fxNyxey5 wXRJL79zB56nl2hMQupfoAqAvFMgDd70PuKIT1suKsUy82J5/Nel9/h+qx4CM7Y6nyK1rhsaB2ZflS WoMoqT6t9kQuFw6ucKuMkEo42oPdXomyQptkOZBq1Zd9BIfPP3u8dKHraI9n+tyFzJA06YTKnr/IWf YXRAvcg99vfyyoP6ia+43+ve4a+hclWNF1LgKpapKLLfkcc2WUcIJQJBO0eq6tqm1uJVmevHwzMJ12 rTv0038+U2qg94UZXlEOyyuL2Aq8k4w== X-KPN-MID: 33|oaSdtL18s0S3rmYtAKo3wUuP64Wro3UI8fc2nbCgSYkZFJ1PIcvm+PDGrnhJnIq Pe58mfy9QcxWMjNND2NoMh/s8ZHM67GgrW6A4SSxGsvA= X-KPN-VerifiedSender: Yes X-CMASSUN: 33|6wtsfzs6BSedgfqbgXrjx0lfIjIgBkINRsDDAaq8ZaMu5vBQCwFuS51AkST6mq4 FDgpvF0pSnSB6B4VrhqmHKA== Received: from daedalus.home (unknown [178.225.116.246]) by smtp.xs4all.nl (Halon) with ESMTPSA id 0c049981-163a-11f1-9c00-00505699d6e5; Mon, 02 Mar 2026 14:16:45 +0100 (CET) From: Jori Koolstra To: Alexander Viro , Christian Brauner , Jeff Layton , Chuck Lever Cc: Jan Kara , Alexander Aring , linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, jkoolstra@xs4all.nl Subject: [PATCH v2] vfs: add support for empty path to openat2(2) Date: Mon, 2 Mar 2026 14:16:50 +0100 Message-ID: <20260302131650.3259153-1-jkoolstra@xs4all.nl> X-Mailer: git-send-email 2.53.0 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" To get an operable version of an O_PATH file descriptors, it is possible to use openat(fd, ".", O_DIRECTORY) for directories, but other files currently require going through open("/proc//fd/") which depends on a functioning procfs. This patch adds the OPENAT2_EMPTY_PATH flag to openat2(2). If passed LOOKUP_EMPTY is set at path resolve time. Signed-off-by: Jori Koolstra --- fs/open.c | 9 ++++----- include/linux/fcntl.h | 5 ++++- include/uapi/linux/openat2.h | 4 ++++ 3 files changed, 12 insertions(+), 6 deletions(-) diff --git a/fs/open.c b/fs/open.c index 91f1139591ab..4f0a76dc8993 100644 --- a/fs/open.c +++ b/fs/open.c @@ -1160,7 +1160,7 @@ struct file *kernel_file_open(const struct path *path= , int flags, EXPORT_SYMBOL_GPL(kernel_file_open); =20 #define WILL_CREATE(flags) (flags & (O_CREAT | __O_TMPFILE)) -#define O_PATH_FLAGS (O_DIRECTORY | O_NOFOLLOW | O_PATH | O_CLOEXEC) +#define O_PATH_FLAGS (O_DIRECTORY | O_NOFOLLOW | O_PATH | O_CLOEXEC | OPE= NAT2_EMPTY_PATH) =20 inline struct open_how build_open_how(int flags, umode_t mode) { @@ -1185,9 +1185,6 @@ inline int build_open_flags(const struct open_how *ho= w, struct open_flags *op) int lookup_flags =3D 0; int acc_mode =3D ACC_MODE(flags); =20 - BUILD_BUG_ON_MSG(upper_32_bits(VALID_OPEN_FLAGS), - "struct open_flags doesn't yet handle flags > 32 bits"); - /* * Strip flags that aren't relevant in determining struct open_flags. */ @@ -1281,6 +1278,8 @@ inline int build_open_flags(const struct open_how *ho= w, struct open_flags *op) lookup_flags |=3D LOOKUP_DIRECTORY; if (!(flags & O_NOFOLLOW)) lookup_flags |=3D LOOKUP_FOLLOW; + if (flags & OPENAT2_EMPTY_PATH) + lookup_flags |=3D LOOKUP_EMPTY; =20 if (how->resolve & RESOLVE_NO_XDEV) lookup_flags |=3D LOOKUP_NO_XDEV; @@ -1362,7 +1361,7 @@ static int do_sys_openat2(int dfd, const char __user = *filename, if (unlikely(err)) return err; =20 - CLASS(filename, name)(filename); + CLASS(filename_flags, name)(filename, op.lookup_flags); return FD_ADD(how->flags, do_file_open(dfd, name, &op)); } =20 diff --git a/include/linux/fcntl.h b/include/linux/fcntl.h index a332e79b3207..d1bb87ff70e3 100644 --- a/include/linux/fcntl.h +++ b/include/linux/fcntl.h @@ -7,10 +7,13 @@ =20 /* List of all valid flags for the open/openat flags argument: */ #define VALID_OPEN_FLAGS \ + /* lower 32-bit flags */ \ (O_RDONLY | O_WRONLY | O_RDWR | O_CREAT | O_EXCL | O_NOCTTY | O_TRUNC | \ O_APPEND | O_NDELAY | O_NONBLOCK | __O_SYNC | O_DSYNC | \ FASYNC | O_DIRECT | O_LARGEFILE | O_DIRECTORY | O_NOFOLLOW | \ - O_NOATIME | O_CLOEXEC | O_PATH | __O_TMPFILE) + O_NOATIME | O_CLOEXEC | O_PATH | __O_TMPFILE | \ + /* upper 32-bit flags (openat2(2) only) */ \ + OPENAT2_EMPTY_PATH) =20 /* List of all valid flags for the how->resolve argument: */ #define VALID_RESOLVE_FLAGS \ diff --git a/include/uapi/linux/openat2.h b/include/uapi/linux/openat2.h index a5feb7604948..c34f32e6fa96 100644 --- a/include/uapi/linux/openat2.h +++ b/include/uapi/linux/openat2.h @@ -40,4 +40,8 @@ struct open_how { return -EAGAIN if that's not possible. */ =20 +/* openat2(2) exclusive flags are defined in the upper 32 bits of + open_how->flags */ +#define OPENAT2_EMPTY_PATH 0x100000000 /* (1ULL << 32) */ + #endif /* _UAPI_LINUX_OPENAT2_H */ --=20 2.53.0